Reaction and Succession in Relation to the Plant Covering. 403 
root systems on which one not infrequently notes the copious development 
of fine rootlets in relation to rabbit faeces, fragments of old Psamma 
rhizomes, &c. For example, the root system of a Silene maritima plant 
growing in sand occupied a volume of over eight cubic feet of sand, and the 
aggregate length of the main roots was over 1 1 ft. (For the exposure 
Text-fig. 3. Root systems of Myosotis collina and a seedling of Senecio jacobaea. (f natural size.) 
of this root system I am indebted to Miss P. Hutchinson.) Here, as in 
other cases, the method adopted was to support the roots in situ by means 
of wire stakes and remove the sand by an air blast. 
Soil Reaction and the Effect of Rabbits. 
The highest p. H. values in the dunes, i. e. the most alkaline conditions, 
are realized in the earliest stages of the succession. The lowest p. H. value 
observed in the young dunes was 6- 9 and the highest 7*4. 
